For the preparation of 4'-O-tetrahydropyranyladriamycin (hereinafter referred to as 4'-O-THPADM in short) b from adriamycin (hereinafter referred to as ADM in short, which has a structural formula (1) as given below), one method is known, as described in Japanese patent publication No. 47194/81. According to this method, ADM is directly tetrahydropyranylated (hereinafter referred to as THP-ated, in short) to obtain a mixture of 4'-O-THPADM a and b, and then the 4'-O-THPADM b is isolated therefrom by chromatography.
The 4'O-THPADM a and b as mentioned in the present invention are stereoisomers with respect to the 4'-position thereof. The absolute structure of these isomers have been determined to be (2"S)-4'-O-THPADM and (2"R)-4'-O-THPADM, respectively (Refer to "Journal of Antibiotics" by Hamao Umezawa et al., Vol. 37, pp. 1094-1097, in 1984.).
For the preparation of the 4'-O-THPADM b from daunomycin (hereinafter referred to as DM in short), two methods are known, as described in Japanese patent application OPI No. 104299/80 and No. 156300/81. (The term "OPI" as used herein means an "unexamined and published application".) ##STR1##
In the above-mentioned three methods, not only the desired compound or 4'-THP-ated-ADM but also by-products or 9- or 14-THP-ated compounds are formed.
The present invention is to solve this problem and to selectively THP-ate the 4'-position only. However, even if the 4'-position is selectively THP-ated, 4'-O-THPADM a which is a stereoisomer is formed as a by-product. The present invention additionally provides a method for the conversion of the 4'-O-THPADM a into the other stereoisomer of 4'-O-THPADM b, whereby the said additional problem can be also solved. Thus, the present invention provides the preparation of 4'-O-THPADM b from ADM with a high yield.